Slip segment inserts for a downhole tool

ABSTRACT

A downhole tool has a plurality of slip segments with buttons extending therefrom. The buttons will engage the well and may be made from material with no magnetic characteristics, for example, silicon nitride.

BACKGROUND

Downhole tools for use in oil and gas wellbores often have drillable components made from metallic or non-metallic materials, such as soft steel, cast iron, engineering grade plastics, and composite materials.

In the drilling or reworking of oil wells, a great variety of downhole tools are used. For example, but not by way of limitation, it is often desirable to seal tubing or other pipe in the casing of the well, such as when it is desired to pump cement or other slurry down the tubing and force the slurry out into a formation. It thus becomes necessary to seal the tubing with respect to the well casing and to prevent the fluid pressure of the slurry from lifting the tubing out of the well. Downhole tools referred to as packers and bridge plugs are designed for these general purposes and are well known in the art of producing oil and gas.

Bridge plugs isolate the portion of the well below the bridge plug from the portion thereabove. Bridge plugs therefore may experience a high differential pressure and must be capable of withstanding the pressure so that the bridge plug seals the well and does not move in the well after it has been set.

Bridge plugs make use of metallic or non-metallic slip segments, or slips, that are initially retained in close proximity to a mandrel but are forced outwardly away from the mandrel of the tool upon the tool being set to engage a casing previously installed within an open wellbore. Upon the tool being positioned at the desired depth, or position, the slips are forced outwardly against the inside of the casing to secure the packer, or bridge plug as the case may be, so that the tool will not move relative to the casing when, for example, operations are being conducted for tests, to stimulate production of the well, or to plug all or a portion of the well.

Cylindrically shaped inserts, or buttons, may be placed in such slip segments, especially when the slip segments are made of a non-metallic material such as plastic composite material, to enhance the ability of the slip segments to engage the well casing. The buttons must be of sufficient hardness to be able to partially penetrate, or bite into, the surface of the well casing which is typically steel. However, especially in the case of downhole tools being constructed of materials that lend themselves to being easily drilled from the wellbore once a given operation involving the tool has been performed, the buttons must not be so hard or so tough to resist drilling or fouling of the cutting surfaces of the drilling bit or milling bit.

Buttons made of zirconia ceramic materials offer to a certain extent the desirable characteristics of being a sufficient hardness to bite in the casing upon setting the tool, but are not so tough as not to be drillable when it comes time to remove the tool from the wellbore. At times the leading edge of the cylindrically shaped buttons made of zirconia ceramic materials may chip or fracture as the slip element engages with the well casing. Many times, such chipping along the leading edge does not degrade the anti-slipping ability of the tool to a level that the tool actually slips in the casing under normal conditions. However, under extremely high pressures or temperatures the undesired chipping could adversely affect the anti-slip performance of the slip elements because the button would not be able to bite as deeply into the casing as would be possible if the leading edge were not chipped during the setting of the tool.

Buttons formed of metallic-ceramic composite (MCC) have been utilized and perform well. MCC materials have a percentage of metallic material in the total composition and have a magnetic property characteristic. Such MCC buttons can withstand and perform at temperature and pressure of up to at least 325° F. and 10,000 psi. Such MCC inserts are, however, more difficult to drill than zirconia ceramic buttons. For example, zirconia ceramic buttons generally break up in small fine pieces when drilled. MCC buttons break into larger pieces when drilled. A drill bit used to drill MCC will experience significantly more wear than when used to drill zirconia ceramic.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section of a downhole tool disposed in a well.

FIG. 2 is an enlarged cross section of a slip segment of the current disclosure.

FIG. 3 is a perspective view of a slip segment of the current disclosure, showing the forward face of the slip segment.

DESCRIPTION OF EMBODIMENTS

A downhole tool has a mandrel and an expandable packer element disposed thereabout for sealingly engaging a well. Slip assemblies are positioned on the mandrel above and/or below the packer element to anchor the downhole tool in the well. Each slip assembly comprises a slip ring movable from an unset position to a set position in which the slip ring engages the well. The slip ring comprises a plurality of slip segments. Each slip segment is retained about the mandrel and is movable radially outwardly so that it will engage the well and anchor the tool in the well. A plurality of inserts, or buttons may be secured to the slip segments, and will extend outwardly from the outer surface thereof to grip casing in the well. The inserts are disposed in cavities.

A retaining ring is disposed about the slip ring to retain the slip ring about the mandrel, and may be received in grooves defined in the slip segments that comprise the slip ring. The retaining ring will hold the slip ring in an unset position, and will prevent the slip ring from prematurely moving outwardly to the set position in which the slip ring grippingly engages the casing to hold the tool in the well.

Referring to the drawings, FIG. 1 shows well 10 comprising a wellbore 12 with a casing 14 cemented therein. Downhole tool 16 comprises a mandrel 18 with an outer surface 20 and an inner surface 22. The tool in FIG. 1 may generally be referred to as a bridge plug since downhole tool 16 has an optional plug 24 pinned within mandrel 18 by radially oriented pins 26. Plug 24 has a seal 28 located between plug 24 and mandrel 18. The overall tool structure would be suited for use as and referred to simply as a packer if plug 24 were not incorporated and fluid communication were allowed through the tool. Other components may be connected so that the packer, without plug 24 may be used, for example, as a frac plug.

A spacer ring 30 is mounted to mandrel 18 with a pin 32. A slip assembly 34 is disposed about mandrel 18 and spacer ring 30 provides an abutment which serves to axially retain slip assembly 34. Downhole tool 16 has two slip assemblies 34, namely a first slip assembly and second slip assembly which are shown in the drawings and are designated in the drawings as first and second slip assemblies 34 a and 34 b for ease of reference. The slip assemblies will anchor downhole tool 16 in well 10. The structure of slip assemblies 34 a and 34 b is identical, and only the orientation and position on downhole tool 16 are different. Each slip assembly 34 includes a slip ring 36 and slip wedge 38 which is pinned into place with pins 40.

Slip ring 36 is an expandable slip ring 36 which has a retaining ring 42 disposed in grooves 44. Retaining ring 42 will retain slip ring 36 in an unset position about mandrel 18 when downhole tool 16 is lowered into the well. Slip rings 36 may be moved or radially expanded from the unset to the set position which is seen in FIG. 1 in which the first and second slip rings 36 engage casing 14 to hold downhole tool 16 in the well. Retaining rings 42 will break as slip rings 36 expand radially outwardly.

Slip rings 36 are comprised of a drillable material and may be, for example, a molded phenolic and have an outer surface 46. Slip rings 36 may be made from other drillable materials as well such as drillable metals, composites and engineering grade plastics. The remainder of the slip assembly and other components of the tool may likewise be made from drillable materials. A plurality of inserts or buttons 48 are secured to slip ring 36 by adhesive or by other means and extend radially outwardly from outer surface 46.

Each slip ring 36 is preferably comprised of a plurality of slip segments 50. Slip segments 50 are shown in cross section in FIG. 2. Slip rings 36 may include, for example, six to eight slip segments 50 that encircle mandrel 18. Slip ring 36 may include more or less than six or eight segments, and the examples herein are non-limiting. A packer element assembly 60 which includes at least one expandable packer element 62 is positioned between slip wedges 38. Packer shoes 64 may provide axial support to the ends of packer element assembly 60.

Retaining rings 42 are disposed about slip rings 36, and may be received in grooves 44. Retaining rings 42 are each comprised of a retaining band 68, and a dampener, or spring suppressor 70. Retaining band 68 can be used, if desired, without spring suppressor 70, in which case retaining ring 42 will simply comprise retaining band 68. Retaining band 68 may be made from a metal, or may be a composite, such as a fiberglass composite retaining band. The examples provided are not limiting, and retaining band 68 may comprise any material, preferably a drillable material, that will provide adequate strength to prevent premature breakage. Dampener 70 may be made from rubber, for example, a nitrile rubber. Other materials that will dampen or suppress the energy, or spring effect of retaining band 68 may be used. Dampener 70 is affixed to retaining band 68 by, for example, bonding, or molding.

Retaining band 68 may be a ring-shaped band 68, and may have a rectangular cross section with outer surface 72. Outer surface 72 may comprise outer circumferential surface 74, inner circumferential surface 76, and side surfaces 78 and 80. Dampener 70 may be affixed to any or all of surfaces 74, 76, 78 and 80, and may, if desired, completely encapsulate retaining band 68.

Slip segments 50 of the current disclosure are shown in FIGS. 2 and 3. Slip segments 50 comprise a slip segment body 51 with first and second ends 82 and 84, which may be referred to as abutment end and free end 82 and 84, respectively. Slip segment body 51 has first and second sides 88 and 90, and a forward, or outer arcuate face 92. An arcuate inner surface 93 will preferably have topology complementary to outer surface 20 of mandrel 18.

Buttons, or inserts 48 are secured to slip segment bodies 51 and extend outwardly from outer arcuate face 92. Inserts 48 are secured in cavities 94. The embodiment shown includes four cavities 94 and four inserts 48 in each slip segment body. It is understood that more or less inserts may be used. The orientation of the buttons is such that when set, the buttons will grippingly engage easy 16. Buttons 48 in the embodiment shown are cylindrically shaped buttons.

Buttons 48 in the embodiment described are made from silicon nitride (Si₃N₄) which contain no metallic material in the composition or have no magnetic properties. Buttons 48 may, for example, be comprised of product SN-235P from Kyocera. Buttons comprised of such materials are more drillable than MCC buttons, and are more akin to zirconia ceramic with respect to drillability. However, silicon nitride buttons, particularly those made from SN-235P, will grip a casing and anchor a tool in a well at temperatures and pressures at least as high as 325° F. and 10,000 psi, like MCC buttons. Thus, the silicon nitride buttons have better drillability than the MCC buttons, while having similar gripping characteristics of MCC buttons.

During testing, tools using silicon nitride buttons have been shown to hold at a temperature of 325° F. and a pressure of 11,000 psi. Using a roller cone style drill bit, the resulting SN-235P insert cuttings were smaller than the MCC cuttings. 

What is claimed is:
 1. A downhole tool for use in a well comprising: a mandrel; a plurality of slip segments disposed about the mandrel and movable from an unset to a set position in the well, the slip segment comprising: a slip segment body; and a plurality of buttons extending outwardly from the slip segment body for engaging the well in the set position, the buttons having favorable drillability characteristics, and being able to withstand well pressures of 10,000 psi at a temperature of 325° F.
 2. The downhole tool of claim 1 wherein the insert buttons are silicon nitride.
 3. The downhole tool of claim 2, wherein the buttons are SN-235P.
 4. The downhole tool of claim 1 further comprising a packer disposed about the mandrel.
 5. The downhole tool of claim 1 wherein the buttons have the drillability characteristics of zirconia ceramic buttons, and the pressure and temperature characteristics of metal composite ceramic buttons.
 6. The downhole tool of claim 1, wherein the inserts are comprised of a material with no magnetic characteristics.
 7. The downhole tool of claim 1, wherein the inserts are comprised of a non-metallic material.
 8. Apparatus for anchoring a downhole tool in a well comprising: a plurality of slip segments disposed about a mandrel of the tool the slip segments comprising: a slip segment body having an outer arcuate face, the slip segment body defining a plurality of cavities; and inserts disposed in the cavities, wherein the inserts have drillability characteristics of zirconia ceramic, and are capable of gripping engagement at well temperatures and pressures of up to at least 10,000 psi and 325° F.
 9. The apparatus of claim 8 wherein the inserts are comprised of silicon nitride.
 10. The apparatus of claim 9, wherein the inserts are comprised of SN-235P.
 11. The apparatus of claim 8, where in the slip segments are movable from an unset to a set position in the well, wherein in the set position the inserts engage a cavity in the well.
 12. The apparatus of claim 11, wherein the inserts have the temperature and pressure characteristics of metal composite ceramic inserts.
 13. The apparatus of claim 8, wherein the inserts comprise a material having no magnetic properties.
 14. The apparatus of claim 8, wherein the inserts comprise non-metallic material.
 15. Apparatus for use in a well comprising: a well comprising: a mandrel; a plurality of sealing elements disposed about the mandrel movable from an unset to a set position in the well; and slip segments disposed about the mandrel and positioned above and below the sealing elements, the slip segments comprising: a slip segment body; and a plurality of buttons extending from the slip segment body, the buttons having favorable drillability characteristics and having no magnetic properties.
 16. The downhole tool of claim 15, wherein the buttons are comprised of silicon nitride.
 17. The downhole tool of claim 16, wherein the buttons are comprised of SN-235P.
 18. The downhole tool of claim 15, wherein in the set position, the buttons grippingly engage a casing in the well. 